We will develop cytotoxic anti-HIV immunoconjugates to eliminate persistent HIV reservoirs. These molecules aim to kill cells producing infectious HIV. Unconjugated (naked) antibodies can kill cells via complement and Fc-receptor mediated effects. We hypothesize that cytotoxic immunoconjugates will prove even more effective than naked mAbs in killing productively-infected cells. They may be used alone if there is sufficient ongoing virus replication during anti-retroviral therapy (ART)-induced clinical latency, or in conjunction with latency-disrupting agents in an ?activate and purge? protocol. There are different forms of cytotoxic immunoconjugates, including immunotoxins, radioimmunoconjugates, and antibody-drug conjugates. Each may have unique advantages or limitations for the treatment of HIV infection. We have described anti-HIV immunotoxins and antibody- drug conjugates, identified the best mAbs for targeting them, and shown anti-viral activity in mice and macaques. We found that while anti-HIV immunotoxins were potentially effective in SHIV-infected macaques, their utility was limited by immunogenicity. Drug conjugates may be less immunogenic, but we found them less potent than immunotoxins, and they may only be cytotoxic in dividing cells. We will optimize the design of anti-HIV immunoconjugates, all based on the same mAbs to HIV Env, then compare the efficacy of the best immunoconjugates with unconjugated mAbs and irrelevant conjugates, using the same assays. To do so, we propose the following Specific Aims: Aim 1. To optimize design of anti-HIV immunoconjugates using cytotoxicity to compare efficacy. We will produce less-immunogenic immunotoxins, more potent antibody drug conjugates and 211At- radioimmunoconjugates and compare them using cytotoxicity on Env-expressing cells. Aim 2. To compare conjugates and naked mAbs using primary cell cultures. We will test the efficacy of immunoconjugates using primary outgrowth cultures from ART-treated patients. Aim 3. To compare conjugates and unconjugated mAbs in HIV-infected, ART-treated immunodeficient mice reconstituted with human hematopoietic tissue. Viremia and tissue virus loads will be quantified and viral integration analyses performed. These studies aim to identify the most effective form of immunoconjugate for future testing as a pre- clinical candidate in SHIV-infected ART treated macaques. These studies also have relevance for the use of immunoconjugates in other conditions, especially cancer.